Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy and is among the most common human genetic diseases. A variety of mini- and full-length dystrophin cassettes can prevent the development of most or all dystrophic symptoms in mdx mice, a model for DMD. These cassettes can be delivered efficiently to adult mdx mouse muscles using several viral vectors, including gutted adenovirus (Ad) or adeno-associated virus (AAV), resulting in a reversal of many dystrophic features. Nonetheless, a major rate limiting step for DMD gene therapy is the ability to target muscles throughout the body. Considerable interest has developed in the use of stem cells, such as hematopoietic and mesenchymal stem cells, to contribute systemically to the repair of muscle tissue. However, transplantation of normal donor cells into a patient entails substantial risks of immune rejection and graft vs. host disease. Performing autologous stem cell transplantation after transduction with an integrating dystrophin expression vector could ameliorate this risk. We propose to develop a variety of lentiviral vectors and explore their ability to transduce bone marrow cells and myogenic precursors. Lentiviral vectors have a 9 kb cloning capacity and can hold both micro- and mini-dystrophins, together with muscle-specific promoters. Lentiviral vectors also integrate into the host cell genome leading to permanent expression for the lifetime of the targeted cell. We will test and compare the ability of these vectors to transduce stem cells and muscle precursors, and to deliver functional dystrophin to muscle following either ex vivo or in vivo gene transfer. We will also explore gene transfer methods to stimulate conversion of non-muscle cells to myogenic stem cells and/or satellite cells, and to drive expansion of myogenic precursors in muscle tissue. Together, these studies will increase the prospects of using stem cell technologies for DMD gene therapy. If successful, these methods could be applied to many different types of muscular dystrophy.